In the standard manufacture of an integrated circuit, typically more than one hundred steps are carried out that involve wafer cleaning or surface preparation. These steps range from removing residues intentionally placed on the surface, such as a post-resist strip/ash residual removal step, to the preparation of a surface for subsequent processing, such as by removing native oxide at a surface, and to etching itself. As a result, a variety of methods to treat surfaces are required.
Most cleaning or surface preparation steps are carried out in the ‘wet’, in other words by treating a substrate with a liquid composition. Typically (but not always), the cleaning effect of an active species is increased with its concentration, and, therefore, in order to maximize the cleaning effect of the liquid composition, the concentration of the active species is ideally maximized. However, due to cost, environmental and safety concerns, cleaning and surface preparation is increasingly being carried out by using dilute compositions. In order to compensate for possible changes in the cleaning effect at lower concentrations, the cleaning or surface preparation may be aided by the use of some form a mechanical energy, such as megasonics or jet-spray processing.
Accordingly, there is a need for chemistries that can be used in both single-wafer and batch processing while addressing a variety of goals in the cleaning or surface preparation process.
One specific cleaning or surface preparation step is the removal of residues containing metallic species. The metallic species may be left on the surface of a wafer substrate after, for example, chemical mechanical polishing, or what is more typically referred to as chemical mechanical planarization (CMP). CMP is described in more detail in Kumar et al., Chemical mechanical planarization for microelectronics, Applications Materials Science and Engineering R 45 (2004) 89-220. Typically, in order to remove these residues, a liquid composition comprising a complexing agent is used. The complexing agent attaches to positively charged metal ion species by coordination through a non-metal atom electron donors such as nitrogen and oxygen functionalities. The resulting complex can serve several functions. For example, if the complex is more soluble than the metal species by itself, it facilitates removal of the metal ion from the surface. Alternatively, if the complexed product is not soluble in solution, it becomes a passivating agent by forming an insoluble film on top of the metal surface.
One problem with current ingredients in semiconductor processing fluids is that they have a tendency not only to serve their intended function, such as the removal of residues from processing, but also can remove both metals and their oxides, such as copper and copper oxide, especially in the case with acidic complexing agents, such as citric acid which can lead to failure of the semiconductor device. Accordingly, there is a need for semiconductor cleaning fluids and processing agents that are not aggressive in this way towards metal substrates, while effectively serving their intended function, such as providing for the chelation of metal ion residues and particles created during the manufacturing processes.